A verbal is a verb that acts like a different part of speech. Infinitives, gerunds, and participles are all types of verbals. An infinitive is a verbal consisting of to + a verb, and it acts like a subject, direct object, subject complement, adjective, or adverb in a sentence.
HeadOn is the brand name of a topical product claimed to relieve headaches. It achieved widespread notoriety in 2006 as a result of a repetitive commercial, consisting only of the tagline HeadOn. Apply directly to the forehead, stated three times in succession.
Heads up as an adjective means being aware. Heads up as the noun is giving someone new information, making them more aware of the situation. Literally having your head up and your eyes open means you're more aware of your surrounding (contrast with the heads down posture of messing with your phone). So a heads-up display for a pilot helps him keep his eyes open and on the sky instead of down at the controls.